Invalid auto-generated container name using Docker provider and a folder that starts with an underscore

[Jaymon]

Running vagrant up in a folder that begins with an underscore (eg, _foo) using the docker provider that does not explicitely set the name attribute results in an Invalid container name error.

Debug output

It's easy to see the problem so I don't think the debug output is needed since the error lies in the auto container name code of the docker provider.

Expected behavior

It was expected for vagrant up to succeed and bring up the docker container with an auto-generated name.

Actual behavior

A Docker command executed by Vagrant didn't complete successfully!
The command run along with the output from the command is shown
below.

Command: ["docker", "run", "--name", "_foo_default_1722722989", "-d", "-v", ".../_foo:/vagrant", "57ed1512823d6c273d82fe84bf974a3f7b833c2065787e655ae9746719f99866", {:notify=>[:stdout, :stderr]}]

Stderr: docker: Error response from daemon: Invalid container name (_foo_default_1722722989), only [a-zA-Z0-9][a-zA-Z0-9_.-] are allowed.
See 'docker run --help'.

Reproduction information

Vagrant version

$ vagrant -v
Vagrant 2.4.1

Host operating system

macOs Sonoma 14.4.1

Guest operating system

Ubuntu 20.04

Steps to reproduce

1. Create a folder that starts with an underscore (eg _foo)
2. Create a minimal Dockerfile in that directory (eg _foo/Dockerfile:

   FROM ubuntu:20.04
   CMD ["sleep", "infinity"]
   

3. Create a minimal Vagrantfile in that directory (eg _foo/Vagrantfile) (see the Vagrantfile section for the contents)

You can fix the error and successfully bring up the docker container by adding to the Vagrantfile's docker config block:

d.name = "foo"

Which bypasses the auto name generating code.

Vagrantfile

Vagrant.configure("2") do |config|

  config.vm.provider :docker do |d|
    d.build_dir = "."
    d.remains_running = true
  end

end